US vice-presidential candidates Joe Biden and Paul Ryan are preparing for their televised debate on Thursday with the knowledge that a strong performance during the head-to-head from Republican presidential candidate Mitt Romney has closed the gap with President Obama to just two points.

Polls over the weekend suggest that the White House incumbent maintained an advantage in the race, but one that has been severely eaten into following a lacklustre performance at Wednesday's debate. An Ipsos/Reuters snapshot of voter intention put Obama ahead on 47% to Romney's 45%.

Biden and Ryan are cramming on each other's positions on the issues and have taken on mock-opponents in debate camps in preparation for their spot in the national limelight.

Already, the Ryan camp has sought to manage predictions. Ryan told reporters last week he expected Biden to come at him like a "cannonball", while Reince Priebus, chairman of the Republican national committee, said on Sunday he expects the Wisconsin congressman to do well but noted that Biden is a talented debater.

"Paul is a smart guy. He has committed his life to understanding the problems of our economy," said Priebus, on CNN's State of The Union. "I think Paul is going to do a great job, but I think it's important to understand" Biden is "a gifted orator" and "very good at rhetoric."

The two men, who vary greatly in experience as well as ideology, will face off for the first time on the public stage on October 11 in Danville, Kentucky, and the stakes are high.

Biden, 69, who has served in the Senate for 36 years and run for president twice, is under pressure to make up some of the ground Obama lost in his widely criticised performance on Wednesday. There was surprise that Obama did not employ attacks he has previously used to good effect in campaign ads and while on the road. There was no mention of Romney's ill-advised quip in which he appeared to dismiss 47% of Americans as welfare-takers who believed they are victims, nor the candidate's record at Bain capital.

Biden is expected to go after his Republican opponent's key arguments on taxes, entitlement reform and deficit reduction.

Ryan also has a tough job ahead of him. At 42, he has 14 years in Congress to Biden's almost four decades and has never debated at a national level. He stands to prove himself as Romney's running mate, while defending his position on taxes.

Analysts predict both men will stick to the issues they have discussed on the campaign trail, while fleshing out some of the themes outlining the differences between them highlighted in last week's debate by Obama and Romney.

However, they have an additional dimension to consider – not getting ahead of the boss.

"The vice presidential candidates have to be a little careful about not getting in front of the news and not getting in front of their top-of-the-ticket partners."

This week, Biden has cleared the decks for an intense "debate camp" in Wilmington, Delaware. He has so far engaged in two mock debates with Chris Van Hollen, a Democratic representative for Maryland, in the place of Ryan.

Ryan ended three days of debate camp in south-west Virginia on Friday, where Ted Olsen, the former US solicitor general, stood in for his Democratic opponent. Playing the role of Martha Raddatz, of ABC, moderator, was Romney's former deputy as governor of Massachusetts, Kerry Healey, according to the Washington Post.

Biden, who has a reputation for gaffes, told reporters last week that he has been carefully studying Ryan's position on the key issues.

"I just want to make sure that when I say these things, I don't have the congressman saying: 'No no no, I don't have that position,' or, 'That's not the governor's position'," Biden said.

Ryan, who told the Weekly Standard last week he expected Biden to come after him "like a cannonball", got his criticism in early, as he said: "He'll be in full attack mode, and I don't think he'll let any inconvenient facts get in his way."